1. Field of the Invention
The present invention pertains to a method and apparatus for manufacturing jewelry, and an article of jewelry made thereby. More particularly, the method and apparatus are directed to the use of an XYZ mechanical table operating under computer control to cut the article of jewelry from a metal workpiece.
2. Description of the Related Art
FIGS. 1A and 1B depict the front and back, respectively, of a generalized article of jewelry having features that typify most articles of jewelry. In the usual case, the article of jewelry is made of metal such as gold, although it will be appreciated that other material such as coated plastic may be used.
The article of jewelry is in the form of a pendant having an outline shape 11, and two openings 12. Together the outline and the openings comprise cutout areas, that is areas that define the perimeter of the pendant, whether the perimeter is an internal or an external edge of the pendant.
The pendant also has a design area 14. Unlike the cutout areas, the design area is a surface feature of the pendant and completes the overall appearance of the pendant by forming a design or pattern on the surface thereof. Design areas are not cut completely through the pendant. Design areas are needed to define various features within the pendant (for example, the top and bottom of the "O" in "MOM"), while preventing these features from separating from the pendant. Thus, design areas do not pass completely through the pendant, and, as shown in FIG. 1B, are not visible from the back of the pendant.
In general, three techniques are known for manufacturing such an article of jewelry: etching, stamping, and casting. Each of these techniques is useful in a particular situation, and each has certain drawbacks. Each method, and its applicability and drawbacks, will be described below.
First, the etching technique will be described with reference to the pendant illustrated in FIGS. 1A and 1B. In general, the etching technique works by forming a negative photoresist image of the desired shape on a sheet metal workpiece (e.g. gold), and etching away unprotected regions of the sheet metal workpiece.
As the initial step in the etching technique, art work for the front and the back of the pendant is generated, and the front and the back are transferred as solid black lines onto clear acetate. As shown in FIGS. 2A and 2B, cutout lines are designated 1, and design lines are designated 2. As further shown in FIG. 2A and 2B, the outline of a frangible link 4 is added at this time. The frangible link will prevent the pendant from completely separating from the sheet metal workpiece during the etching process. Thus, the pendant will remain attached to the sheet metal workpiece and will not fall to the bottom of the etching solution. This aids in the final finishing and collection of pendants.
The workpiece is coated on both sides with a photoresist material. The photoresist is a well known dry application type, which is coated onto both sides of the workpiece. The photoresist material reacts when exposed to light. Unexposed material may be rinsed away in a solvent, whereas exposed photoresist material will remain on the surface of the workpiece.
Starting first with the sheet of clear acetate having the pattern illustrated in FIG. 2A, the sheet of acetate is held tightly against a first surface of the workpiece and exposed to light. Then, reversing the metal sheet, and carefully aligning the workpiece with respect to the already-exposed first surface, the sheet of acetate having the pattern illustrated in FIG. 2B is held tightly against the reverse surface and a similar exposure step is performed on the back of the gold sheet.
The workpiece is then dipped in solvent, which removes those portions of the photoresist that have not been exposed to light. This essentially results in a negative image of the patterns illustrated in FIG. 2A and 2B on the front and back surfaces of the workpiece. With a typical jewelry pattern, such as the illustrative pendant being used here, most of the gold sheet is now protected with developed photoresist, and only areas corresponding to cut-out lines 1 and design lines 2 are left unprotected.
The exposure process, however, is imperfect, and requires touch-up. This is a manual step and is performed by carefully observing the developed photoresist on the gold sheet and applying with a fine brush additional photoresist to those areas which should have been, but were not, protected.
At this point, a cross section along line A--A in FIG. 2B through the workpiece is as depicted in FIG. 3A. In FIG. 3A, the workpiece is denoted by reference numeral 8, and the developed photoresist is denoted by reference numeral 3. Cutout areas 1 are unprotected from both sides of the workpiece, while design areas 2 are unprotected only from the top of the workpiece.
The workpiece with the photoresist pattern is then immersed in an etching bath. The workpiece remains in the etching bath for the period of time necessary for the etchant to remove approximately one-half the thickness of the sheet. At this time, a cross-section through the workpiece is as depicted in FIG. 3B. There, it can be seen that cut-out lines 1 have been dissolved from both sides of the workpiece and meet in the center of the workpiece. On the other hand, design lines 2 are only etched from the front of the workpiece, and are therefore only approximately one-half through the workpiece.
After the etching time has expired, the workpiece is removed from the etching bath and the photoresist layer removed by solvent. Frangible link 4 is broken to remove the pendant from the workpiece, and the pendant is polished to a finished state.
While the etching process is relatively straight-forward, there are a number of disadvantages. Primarily, etching is only suited for relatively thin materials. That is, if the etching period lasts too long, the etchant begins to attack the photoresist material itself. Thus, etching is used primarily for thin articles of jewelry.
Further, as well as being suited for relatively thin articles, the etching process is only well-suited for etching pure materials. That is, etching does not work well on layered materials such as gold layer. For example, FIG. 4 shows a base material 5 layered on both sides with gold layer 6. Typically, the base material will be a gold-colored material such as brass. In any event, the etching rates for the gold and the base materials are different. Thus, during the etching process, the arrangement shown in FIG. 4 is obtained. In particular, it can be seen that the base material 5 has been etched to a greater extent than the gold layer 6. At the edges of the finished article, this results in an undesired undercutting of the pendant at those portions corresponding to cut-out lines 1. Further, when two etching portions are in close proximity, a weak link such as shown at 9 may result.
There are a number of other disadvantages. For example, the front to back alignment of the pattern is critical, and if the alignment is not well performed, the process will not work. Further, recovery of gold dissolved during the etching process is complicated and time-consuming, and it involves a number of steps such as precipitation of the gold, collection of the gold precipitate, and refining. All of these steps are time-consuming and involve costly chemicals.
Further, with the simple etching process described above, only one level of design may be obtained. That is, unless multiple photoresist application steps are performed, design areas in the finished article are all the same depth and all constrained to be approximately one-half the depth of the gold sheet, corresponding to the time that the gold sheet is in the etchant bath.
Finally, the overall turn-around for the process is long. In particular, changes to the design are not easily made and such changes require a full repetition of all of the above steps.
The second known method for producing articles of jewelry is the stamping method, and will be described with respect to FIGS. 5A and 5B.
As shown in FIGS. 5A and 5B, the stamping method entails the preparation of two dies, a front die (FIG. 5A) with the desired design inscribed thereon, and a punch-out die (FIG. 5B) defining the perimeter of the article.
The design lines are formed by raised pieces of metal in the die and are transferred to the workpiece by stamping.
The punch-out die shown in FIG. 5B comprises only cut-out lines 1. The cut-out lines are formed in the die so as to enable the finished pendant to be punched from the workpiece.
To fabricate a pendant using the stamping method, the workpiece is initially brought to a design impressing station where the die shown in FIG. 5A is forcefully brought into contact with the surface of the workpiece, thereby to impress its design on the workpiece. Subsequently, the workpiece is brought to a punch station, where it is carefully aligned with the design already formed on the sheet. The punch-out die shown in FIG. 5B is forcefully brought down on the gold sheet, thereby separating the pendant from the gold sheet.
While the stamping method is quick and easy to automate, it suffers from several disadvantages. For example, like the etching method, the stamping method is unsuitable for thick pieces. Further, the method is relatively inflexible, and if a new design is required, both a new die and a new punch-out die are required. The preparation of these dies, is, of course, time-consuming, expensive, and not well suited for automatic processing.
While the stamping process does not suffer from the gold recovery problems of the etching method (since scrap gold is already in the form of a gold sheet), the stamping method is relatively inefficient in its use of the full surface area of the gold sheet. That is, whereas the etching method can virtually fill a gold sheet with patterns of jewelry, the stamping method requires a certain minimum area on the gold sheet for grasping the sheet during the stamping process. Further, the gold sheet cannot be stamped to an extent so as to weaken the gold sheet, since such weakening would not permit the sheet to be held firmly for subsequent stamping processes.
Finally, the stamping process gives an undesired drawn-down shape to the edges of the finished piece. Thus, as shown schematically in FIG. 6, the edge of the finished article after stamping has been drawn to a sharp edge 10 by the punch-out die. This edge must be removed manually, a process that is time-consuming and inconvenient, especially for internal punched-out portions such as portions 1A in FIG. 5B. That is, internal punched-out portions 1A are relatively inaccessible and are often very fine.
The third known method for producing jewelry is the casting method, commonly called the "lost wax" method.
In the casting method, a model of the finished article is prepared from a suitable material, usually paraffin or wax. A master is then formed by encasing the model in a second suitable material, for example, plaster or clay. The master is cut in half, and the model removed from the interior of the master. The interior of the master is polished, and imperfections during the molding process are removed.
From the master, several wax models are created. All the wax models are encased in a plaster mold leaving a suitable sprue for the introduction of molten metal. The plaster mold is heated, thereby melting the wax models which flow out of the sprues.
Molten metal is then poured through the sprues into the vacancies left by the melted wax models. The mold is cooled and the jewelry articles are freed from the mold. The jewelry articles are then finished, for example by polishing their surfaces.
The casting process is a complex and time-consuming process that is relatively unsuited for thin pieces of jewelry. The process is work-intensive, and the cost is high. Special expertise is required to form the masters and molds, and, in any event, the process is unsuited for high volume work. The surface of the molded article invariably needs polishing, since the casting process does not leave a smooth finish on the article. Again, this is a one-at-a-time process requiring special skill and expertise. Finally, the process is not amenable to design changes. That is, any change necessitates the creation of a complete new model, a new master, and a new mold.
To summarize, the three known processes are all relatively work intensive and involve too many manual steps. The recovery of unused gold is uncertain, and many of the processes are unsuitable for use with certain materials. Turn-around time from a new design, or design change, to a finished article is high, and the process is not flexible. Alignment of cut-out portions and design portions is often critical. Additionally, from the above description, it will be appreciated that only solid pieces of jewelry can be created by the casting process. That is, it is not straight-forward to provide a finished piece of jewelry consisting of a base material such as brass surrounded by a gold layer.